US2005244863 discloses a configuration for excitation of luminophores by means of an evanescent wave. An evanescent wave is a rapidly decaying electromagnetic field which cannot propagate due to a sub-wavelength aperture. In this disclosure, exciting radiation is provided to penetrate as an evanescent wave in a bio-molecule containing mixture. The evanescent wave is created by a structure having sub wavelength apertures. However, the apertures only allow a small portion of the generated radiation to be transmitted. This causes a limited yield of luminescent light to be used for detection purposes.